The high resolution scanning transmission electron microscope (STEM) will be used to study the structure of biologcal membranes. A cold stage operating below 10 K will be constructed to study the movement of heavy metal atoms as a function of temperature. The purple membrane of Halobium Halobacterium will be reacted with platinum reagents to achieve specific attachment of individual platinum atoms and the atomic positions will be characterized biochemically. The platinum atoms will be visualized in the STEM at low electron dose by digital image processing of the crystalline purple membrane fragment images. The platinum atoms can be individually visualized at higher electron doses. The effect on biological membranes of adsorption to microscopy support films will be studied. Support films of aluminum, beryllium, and boron will be studied in adsorbing lipid bilayers, bilayer vesicles, and erythrocyte ghosts. Erythrocyte ghosts, and ghosts selectively depleted of some proteins will be studied to find a basis for interpretation of unstained, unfixed membrane preparations and to learn the structure of the cytoplasmic side protein.